Last Sunday, Clinton was at a September 11 memorial ceremony in New York City when she fell ill and had to leave early. She stumbled and appeared to faint while being helped into her campaign van, and it was later revealed she had pneumonia.

Clinton, the Democratic presidential nominee, took three days off from the campaign trail to rest and recover. She returned to campaigning Thursday in Greensboro, N.C.

Clinton's medical problems have been the source of much discussion this week, with critics wondering whether she's healthy enough to serve as president.

Republican presidential nominee Donald Trump appeared on "The Tonight Show" Thursday and made headlines by messing up Trump's hair.